A5 Meaning of A5 in English A5 /ˌeɪ ˈfaɪv◂/ BrE AmE noun [uncountable] a standard size of paper, used in Europe and Japan. A5 paper measures 148 x 210 ↑ millimetre s ⇨ A3 , A4 Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012